This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. We started studying lipid-protein interactions using WALP and KALP peptides. These alpha-helical transmembrane peptides, with a hydrophobic sequence of leucine and alanine of varying length, are flanked at both ends by two tryptophans or lysines as membrane anchors. WALP: Ac-GWW(LA)nLWWA, for example for WALP23 n=8, and KALP: Ac-GKK(LA)nLKKA. These peptides, unlike natural peptides previously studied in our group, can be synthesized in a variety of alpha-helical lengths. It will allow us to engage in a systematic study of the role of hydrophobic mismatch between the peptide length and the lipid bilayer thickness. Studying lipid-protein interactions from the standpoint of hydrophobic matching/mismatching is a familiar approach for our group;see for example our study of Gramicidin A in a variety of lipid phases. Use of several of peptides with different alpha-helical length in the same lipid phase will allow us to separate specific effects of hydrophobic mismatch from effects of lipid environment, in general. Our primary interest is the effect of hydrophobic mismatch on helical tilt and aggregation number WALP/KALP peptides in model membranes.